Taking another look at the atmosphere

Even on a relatively calm day, the Earth’s atmosphere is a swirling mix of gases that react faster than the human eye can see. In order to model these reactions, scientists have generally simplified the problem by treating them as occurring sequentially. However, a new study by researchers at the U.S. Department of Energy’s Argonne National Laboratory and two universities in the United Kingdom demonstrates a new method for obtaining more accurate measurements of these atmospheric processes.

In order to calculate the mathematics of how chemical reactions proceed, called reaction rate coefficients, scientists had by and large looked at the interaction of molecules that were in “thermal equilibrium,” meaning that the internal energies of the molecules are determined only by the temperature.

According to Argonne chemist Stephen Klippenstein, however, this approach neglects the real-world properties of these reactions. “The standard model of sequential thermal reactions would predict the wrong chemical products,” he said.

“It’s like trying to line up a billiards shot when the cue ball is zooming around the table while still acting like it’s standing still,” he added. “It’s a little different because it’s vibrational energy instead of translational energy, but the basic problem is similar.”

Only by ascertaining the correct rate coefficients can scientists create models that accurately calculate the proportions of different atmospheric gases, Klippenstein said. Large atmospheric models can rely on thousands of different rate coefficients that characterize these reactions. In the experiment, Klippenstein’s British colleagues looked at the oxidation of acetylene, a common hydrocarbon, to verify the theoretical chemical predictions.